1. Field of the Invention
The present invention relates a recording apparatus which records an image on a recording medium, and more particularly, to a recording apparatus which records an image on a recording medium by discharging liquid from a recording head apart from the recording medium.
2. Related Background Art
Conventionally, in a serial ink-jet printer acting as one of serial-type recording apparatuses, a recording sheet being a recording medium is conveyed by an optimum amount on a platen of supporting the recording sheet by a conveyance roller acting as a conveyance means and a pinch roller rotatively driven according to the conveyance roller. Moreover, a recording head acting as a recording means positioned apart from the recording sheet and for discharging liquid ink to the recording sheet is mounted on a carriage acting as a carrier means of the recording head, and an image is recorded on the recording sheet by discharging the liquid ink from at least one discharge opening array (i.e., a nozzle array) of the recording head while scanning the carriage in the direction (main scan direction) intersecting the conveyance direction of the recording sheet. Under the condition that it is demanded to record a high-quality image, recently, an interspace (hereinafter, called a sheet space) between the recording head and the recording sheet becomes narrow. This is because,. by narrowing the sheet space, it aims to shorten the distance and time until an ink droplet discharged from the recording head is impacted and to minimize a dislocation amount between the ink droplet impact position and a target position.
However, as the sheet space is made narrower, it is highly possible that the recording head collides with the recording sheet when the motion of the recording sheet becomes unstable, the ink adhered on the face of the recording head is thus transferred to the recording sheet and therefore the image quality on the recording sheet is deteriorated. Moreover, it is highly possible that the recording sheet is caught by the recording head and the carriage on scanning and thus it is damaged. Also, it is possible that the recording head collided with the recording sheet is damaged and thus normal recording becomes unguaranteed.
In the above ink-jet printer, especially the right and left ends of the recording sheet easily float, whereby there is a high possibility that these ends collide with the recording head. Moreover, in the structure of the serial-type recording apparatus, the motion of the recording sheet is relatively stable while the recording sheet is being pressed and conveyed between the pinch roller positioned on the upstream side of the recording head in the conveyance direction and a spur positioned on the downstream side thereof. However, when the recording is performed on the leading and trailing ends of the recording sheet in the conveyance direction, it is difficult to hold down both the leading and trailing ends of the recording sheet on the upstream and downstream sides of the recording head, whereby there is a high possibility that the recording sheet floats and thus collides with the recording head.
In the ink-jet printer, to prevent the collision of the recording head and the recording sheet, various countermeasures have been considered so far. First, areas other than the area where the image is to be recorded at the right and left ends of the recording sheet, i.e., margins not including the recording area on the recording sheet, were addressed. Thus, a plate member (i.e., a recording sheet floating prevention member) of which the length is equal to or longer than the length of a nozzle array acting as the ink droplet discharge opening array of the recording head, is arranged at the position corresponding to the margin on carriage scanning when the recording sheet is conveyed to the position opposite to the nozzle array, thereby preventing the floating of the side ends of the recording sheet.
On one hand, with respect to the recording to be performed on the leading end of the recording sheet, the rotation axis of the pinch roller is disposed closer to the side of the recording head (on the downstream side of the recording sheet in the conveyance direction) than the rotation axis of the conveyance roller so that the leading end of the recording sheet is pressed against a platen by the pinch roller, thereby preventing the floating of the recording sheet. Moreover, with respect to the recording to be performed on the trailing end of the recording sheet, the rotation axis of the spur rotating according to a sheet discharge roller is disposed closer to the side of the recording head (on the upstream side of the recording sheet in the conveyance direction) than the rotation axis of the sheet discharge roller, or the height of the sheet discharge roller on the downstream side is made higher in a case where the two lines of discharge rollers are provided, so that the trailing end of the recording sheet is pressed against the platen, thereby preventing the floating of the recording sheet. Moreover, the height of a sheet discharge tray is made higher by an optimum amount to prevent the sheet from hanging down, thereby preventing the floating of the recording sheet within the recording area from the sheet discharge roller as a starting point.
In the above countermeasure to prevent the floating of the leading end of the recording medium in the conventional ink-jet printer, a recording medium floating prevention effect is great because the pressing force of the pinch roller to the platen is large. However, the trailing end of the recording medium easily floats because the pressing force to the platen is small. For this reason, if the side ends of the recording medium, particularly the side ends on the upstream side in the conveyance direction, are not pressed by the floating prevention member, there is a problem that a possibility that the trailing end of the recording medium after having passed the pinch roller and being most far from the spur and the discharge roller on the downstream side in the conveyance direction collides with the recording head, becomes higher.
On the other hand, when so-called non-margin recording to perform the recoding throughout the recording sheet is performed, the side ends of the recording sheet are used as the recording area, whereby it is difficult to provide the recording sheet floating prevention member on the margin outside the recording area on the carriage scanning. As a result, there is a problem that the recording sheet easily collides with the recording head.